Perhaps usage of mole 2 is beyond the comprehension of mole 1 (who we don't expect to be well, well educated).

Teapot 1: At least I stay the same all the time, unlike you, moving around and being so disgusting!

Mole 2 is actually a representation of a universal constant (Avogadro constant). Mole 1 moves around and is considered a pest.

Day 2 (one more clue)

Teapot 3: How are you doing?
Teapot 1: You aren't supposed to be here!
Thus said Mole 2 to Mole 3 who is a spy.
Teapot 3: You just knew? Hah!
Teapot 2: How much did you find out!?
A question which mole 3 would not prefer to answer as mole 1 is apparently not the boss or even on the same team! [just so that there's no confusion: Teapot 2 is mole 1 (animal), teapot 1 is mole 2 (constant) & teapot 3 is mole 3(spy)].

Teapot 1: What's with you and your slimy things?
Teapot 2: I help maintain the ecosystem! What about you, only existing in the minds of others?

I am a worm (short for earthworm). And yeah, I am slimy, and it is well-known how I help maintain the ecosystem.

Teapot 1: Hey! I exist in books, magazines, everywhere! I'm so big, more than most can perceive!

I am a worm too. [COMPUTING]
a self-replicating program able to propagate itself across a network, typically having a detrimental effect.
Perhaps the allusion to books, magazines, everywhere pertains to (entities in) cyberspace.

Teapot 2: But you're usually used for things I can't even see!

The activity of a [computer] worm cannot be seen by an earthworm.

Teapot 1: At least I stay the same all the time, unlike you, moving around and being so disgusting!

Typically, a computer worm replicates itself and so it stays the same, even in a copy, in that sense. The earthworm moves around with its slimy body and is considered disgusting.